This invention relates generally to shoring devices used to support the sidewalls of deep narrow excavations and particularly to those utilizing a hydraulically operable expansion device to exert a retaining force against the sidewalls of the excavation.
In the situations in which a deep, relatively narrow excavation or trench is dug for purposes such as routing of sewers, pipes, gas systems or underground cables, a problem arises in that the material forming the soils through which the excavations are undertaken, frequently is subject to the likelihood of being displaced from the sharp vertical walls of the trench. This problem is particularly critical in operations which require that labourers or craftsmen must operate within the trench to carry out necessary activities. In such circumstance, the potential for cave in or fill in of the trench sidewalls may place the lives of the workers within the trench in jeopardy.
These and other problems in the operations of such trench excavations have caused practitioners in the art of constructing shoring devices to improve the traditional timber fabrication shoring devices by using the more modern metal sidewall constructions which vary greatly in construction detail, but generally comprise substantially vertical reinforcement members placed along the trench sidewalls, generally in a top to bottom orientation which are used in combination with and connected to interspaced expandable members. The latter which are operative to exert an outward force against the shoring devices and the trench sidewalls in order to retain the soil and prevent cave in of the sidewalls.
The expandable reinforcing member used in such shoring devices has in the past been fabricated using either of two popular techniques. The first, an example of which is set forth in U.S. Pat. No. 3,393,521 sets forth an expandable member in which a screw type expander mechanism is utilized. In the system shown, an externally threaded shaft is terminated at one end in a load bearing surface. In operation, expansion of the shoring member takes place by rotating the threaded collar with respect to the threaded shaft, causing the threaded shaft to be forced out of the collar.
To meet this problem, practitioners in the art have devised a second expandable member technology in which an expandable hydraulic cylinder coupled to a source of hydraulic fluid under pressure is operative to hydraulically force to load bearing ends of the cylinder member in opposite directions, and exert the appropriate retaining forece against the shoring structure. While a number of such devices have been constructed in the art and their constructions differ in some subtleties, all generally comprise a hydraulic cylinder having a piston within a cylinder and a pair of load bearing surfaces attached one to the cylinder and the other to the piston. A port introduces hydraulic fluid under pressure to the cylinder interior and the pressure of the hydraulic fluid is exerted against the piston driving the piston within the cylinder, thereby creating an expansion under force. U.S. Pat. No. 3,404,533 sets forth such a hydraulic device in which a linkage arrangement couples the hydraulic devices to a pair of vertical shoring members in a pivotal manner and in which means are provided to lock the shoring rails and expandable members in place once installed. Similarly, U.S. Pat. No. 3,347,049 sets forth a hydraulically operable shoring device in which a similar structure to the 533 patent is shown with the advantage that a releaseable coupling is used in connecting the expandable cylinders to the shoring rails. By way of further refinement, U.S. Pat. No. 3,362,167 sets forth a hydraulically operated shoring device in which an oversleeve surrounds the hydraulic cylinder and piston arrangment and acts as a protective device while adding further strength to the hydraulic cylinder for side loading and impacts. Finally, U.S. Pat. No. 3,230,720 sets forth a hydraulically operable shoring device in which a pair of shoring rails are pivotably coupled to expandable hydraulic cylinders in a similar manner to the devices set forth above with the further refinement that means are provided for limiting the angle between the expandable cylinders and the shoring rails to the right angles.
While such combination expandable cylinders and shoring rail devices, as shown in the above referenced prior art, work satisfactorily in the majority of applications, there exists a need in the art for a more lightweight, easily assembled hydraulic expansion cylinder having increased ease of installation and withdrawal.